Method of multi-coloring sealed anodized aluminum



Jan. 9, 1962 A. CYBRIWSKY ETAL 3,016,293

MEIHOD OF MUL'IfI-COLORING SEALED ANODIZED ALUMINUM Filed July 29, 1957 OF A METAL ARTICLE OXIDIZING THE SURFACE LAYER OPTIONAL SEALING l RINSING ETCHING v SELECTED AREAS OF OXIDE LAYER i RINSING i-F Y INVENTOR. ALEXANDER GYBRIWSKY GERALD L. HAGER THEIR ATTORNEY United States Patent '0 Louisville,

' Rich- This invention relates to a method of decorating a metal surface with multi-colored patterns.

At the outset, it should be understood that an anodized aluminum surface may be sealed off in either of two ways, viz: by masking it with an overlying coat or cover; or by sealing it with a sealer of the hydration type to close its pores.

The current practice of decorating anodized aluminum with a plurality of colors is to mask the entire surface except that portion which is to receive the first color, dip the masked aluminum into the first color solution to color the unmasked areas, remove the first mask, again mask all of the surface except that portion which is to receive the second color, dip the aluminum into the second color solution to color the unmasked areas and remove the second mask. The operations of masking, dyeing and unmasking, which are repeated for each additional color,

are time-consuming because the surface must be dried before the masking material may be safely applied and the masking must be removed from the surface by organic solvents and the solvents, in turn, removed before the surface can be placed in a dye bath.

Accordingly, important objects of this invention are: a

to provide an unusually rapid procedure for decorating" an anodized aluminum surface with multi-colored dyes; to eliminate the necessity of masking; to provide a novel process by which a plurality of colors may be readily applied in simple or intricate patterns of precise boundaries; and to provide a process wherein all liquid treatments may be conducted in aqueous media.

These objects are achieved by etching a desired pattern into a hydration sealed anodized or other micro-porous surface to remove the seal and thereby render the unsealed portion capable of absorbing the coloring material, and then applying the coloring material to the entire surface. Starting with the hydration sealing step, this procedure may be repeated for each new color added to the surface.

With this arrangement, an unsealed pattern is formed on an otherwise hydration sealed surface. When this surface is dipped into a dye solution, the dye will coat the entire surface but it will be absorbed into the unsealed portion only. As a consequence, it may be dipped into a rinse or otherwise treated to remove the dyestuff from the sealed portion of the surface without appreciably removing that which has been absorbed by the unsealed surface. The color pattern, which remains after the rinsing step, can be locked within the surface simply by hydration sealing that surface.

Now the process of selectively etching, dyeing and sealing can be repeated for each additional color.

The invention is illustrated in the accompanying drawing which contains a flow diagram of a preferred mode of practicing the process. The reference in the fiow diagram to the step of sealing and any unqualified reference in this specification to a seal or sealer is intended to designate the use of a seal or sealer of the hydration type. Sealers of this type operate to close the pores in the anodic films of aluminum surfaces by the act of swelling the aluminum oxide, forming the surface, either alone or in combination with the deposition of material inside of the pores.

Patented Jan. 9, 1962 ice 2 FLOW DIAGRAM The flow diagram indicates a process for applying two colors, starting with a sheet of metal such as aluminum which has not been anodized. This process, which may be divided into two parts, one for each color, comprises: (1) a first 'part wherein the aluminum surface preferably is successively anodized, dyed and sealed; and (2) a second part wherein the sealed surface is successively etched, dyed and sealed. The flow diagram also indicates the rinsing steps which necessarily follow the steps above noted. The firstpart of the flow diagram is optional. The second part of the invention may be repeated for each additional color desired.

Part I Anodizing and rinsing.--The aluminum surface to be decorated may be provided with an oxide coating by conventional anodizing treatment or by any other well known chemical treatment for producing a microporous film on a base aluminum surface. Conventional anodized films range in thickness from about 0.0001 to about 0.0008 of an inch and these conventional films are entirely satisfactory in practicing the present invention. Before the film is formed, the surface may undergo any of the various well-known surface treatments such as brightening, polishing, etc., in order to influence the final appearance of the product in some desired way. The anodizing operation preferably should be followed by a rinsing step before the dyeing step. V

Optional dyeing and rinsing steps.Since the anodized surfacehas not been scaled, it will readily absorb a coloring material such as a dye. Accordingly, the surface is immersed in a dye bath for an interval of time required to permit the dye solution to soak into the microporous coating. The dye solution used may comprise any of those conventionally employed in coloring aluminum oxide or anodized surfaces such, for example, as diazo dyes, pythalocyanine dyes and inorganicmaterials, such as ferric ammonium oxalate, zinc acetate followed by potassium dichromate, and potassium ferrocyanide followed by ferric chloride.

The time required for this color application varies from a short dip of the surface into the dye solution one or more times and promptly removing it--to a prolonged dip time during which dye is adsorbed in the pores of the anodic coating.

The dye solution is preferably followed immediately by a rinsing treatment to remove excess dye solution from the article since an excess would contaminate the liquids used in subsequent treatments. However, it maybe noted that the anodized surface will not release the absorbed solution very readily during rinsing; hence, an effective color coat will be retained within the pores of the surface.

Sealing and rinsing-After the optional color application, the micro-porous surface of the article is sealed. The purpose of sealing is to close the surface to the degree necessary to protect it against subsequent color contamination in those areas. where further coloring is not desired. The sealing required at this intermediate stage. of the process may be much lighter than that required in finally sealing the product. The seal here, once satisfactory colors are obtained, need not be anything heavier than that required to protect those colors against contamination whereas the final seal must be Available also are other'sealing media, such as solutions,

of horic acid and of sodium chromate or dichromate.

Ordinarily, a heavier seal, such as that provided by immersing the treated surface in hot or boiling water baths, for substantially longer periods, say 20 minutes or longer, is not desired at this stage of the process because it is more chemically resistant and difficult to remove. The sealing operation is preferably followed by rinsing to prevent contamination of the solutions used subsequently in the process. Upon rinsing, the product is ready for the second part of the process.

1 Part II In this part of the process, the surface is selectivelyetched, dyed and sealed.

Selective etching and rinsing-The sealed surface produced by Part I of the process is incapable of absorbing conventional coloring materials until the seal is removed or broken. -According to the present invention, the sealing material is removed or broken at areas forming any desired color receiving pattern. This is accomplished by printing or otherwise applying the etchant in the desired pattern to the surface. This etchant chemically attacks the sealing material and transforms it to a water soluble product which may be removed by rinsing with water. The etchant also removes the coloring material underlying that sealing material.

In general, the degree of etching may be regulated by controlling the deposit time and strength of the etching composition. An important consideration, in the use of the etching material, is to remove the seal on the film without permitting the etching composition to attack the oxide film to any substantial degree. For obtaining colors of uniform shading, it is necessary to obtain uniform etching action. Thus, when appreciable time is expended in the application of that etchant, it should be formulated, as to strength, in consideration of the time needed for. applying the composition to the work, and also in consideration of the time needed to transfer pieces through an etch-removing or rinsing station,

When the etching period is a minute or less, it is important to roll, print or otherwise apply the etchant t the surface very quickly. However, slow acting etchants may be used to advantage in some cases where the surface is large or the mode of application is necessarily slow.

The consistency of the etchant is an important factor in obtaining sharp accurately-placed boundaries between colored sections. Preferably, the etchant is provided as a paste adapting it for application by rolls, spray gun, brush, stencil, or stamp. Exemplary of a paste-type etchant is one containing 25 parts gum arabic, 2.5 parts hydrochloric acid. 7.5 parts of hydrofluoric acid, and 65 parts of water. This composition is a relatively fast acting etchant which should not be left on a lightly-sealed aluminum oxide coating more than about a minute. Ordinarily it is effective within a period as low as 30 seconds.

Another similarly acting composition comprises 34 parts of gum arabic, 18 parts of hydrochloric acid, and 48 parts of water. Although gumarabic was the thickening agent used in the two etching compositions described above, other materials such as methyl cellulose, ethyl cellulose, hydroxy ethyl cellulose, gelatin, tragae canth, and others may be used for this purpose.

Another satisfactory etchant may be compounded of 5% methyl cellulose, 1% glycerin, 25% hydrochloric acid, hydrofluoric acid and water. The proportions and the ingredients of the etchant may be changed within wide rangesto obtain desired etching strengths, viscosities and other properties. As sharper colors are obtained from bright aluminum oxide surfaces, the etching composition may include also brightening ingredients, such as sulfuric and phosphoric acids.

In general, it is desirous to stop the action of the etching composition promptly at the end of the etching period by rinsing vigorously with water in order to assure that the pores of the surface are washed free of the etchant.

The effective cleaning of the porous pattern is desired in order to obtain colors of good brilliance and fastness.

Dyeing and rinsing.-The anodized aluminum article with its porous pattern is now ready for receiving a coloring material capable of permeating the unsealed area. The application of such a material may be accomplished by placing the article in a conventional dye bath which again contains any one of the dyes conventionally employed in coloring anodized aluminum surfaces. After one or more periods of immersion suitable for developing a desired depth of color, the article is removed and rinsed. The surface will, of course, absorb the coloring solution only in the porous pattern area, the remaining portion of the surface being protected by the sealing material against further coloration and against any leaching of the color already locked within it.

Scaling and rinsing.The sealing operation is performed to provide a light seal or a heavy seal. A light seal is provided if the selective etching, dyeing and sealing steps are to be repeated to apply another color. A heavy seal is used if the product is in its final form and a surface protection for serviceability is required. A light seal may be obtained as before. A heavy or permanent seal may be obtained by immersing the article in a hot /2 to 1% nickel or cobaltacetate bath for at least 2 minutes, and then immersing it for 20 minutes or more in a water bath maintained at boiling temperature or a temperature closely thereunder.

Some modes of practicing the invention are illustrated by the three following examples, each of which add one color to the same product.

EXAMPLE I nor sealed may be processed as follows: anodize it for 1 hour to provide an aluminum oxide film approximately 0.0006 of an inch thick; rinse to remove all acid; seal for 1 /2 minutes in a bath of /z% nickel acetate solution having a temperature of to C.; rinse and dry; etch (with an etchant comprising 25 parts gum arabic, 2.5 parts hydrofluoric acid, 7.4 parts hydrochloric acid and 65.1 parts water) over one set of stripe-like areas for 40 seconds; rinse by spraying with unheated tap water to purge it of the etching solution; dye it black by immersion in a bath of black dye (Sandoz Black 0A, manufactured by the Sandoz Chemical Works, Inc.), for 10 minutes; rinse in unheated tap water to remove the excess dye; seal in said nickel acetate bath for 2 minutes; and rinse and dry.

Example I produces an aluminum panel having the characteristic silvery appearance of anodized aluminum with a pattern of black stripes.

EXAMPLE II Process the panel product of Example I as follows: etch it (with the same etchant) over a second set of stripe-like areas for one minute; rinse; dye it blue by immersion in a bath containing 10 grams per liter of blue dye (Sandoz Blue B, manufactured by the Sandoz Chemical Works, Inc.) for 4 minutes; rinse; seal in said nickel acetate bath for 3 minutes; and rinse and dry.

The treatment in Example 11 does not alter the characteristic anodized appearance of the panel nor does it change the black stripes produced in Example I. However, it does add blue stripes to that panel so that the product now has a three color effect.

EXAMPLE III Treat the panel product of Example II as followsz-etch it (with an etchant comprising 50 parts of gum arabic, 22.2 parts of hydrochloric acid and 77.8 parts of water) for 4 minutes; rinse; dye it gold by immersion in a bath of ferric ammonium oxalate; rinse; seal in said nickel acetate bath for 5 minutes to provide the gold area with a temporary seal sufficient to protect it against infusion with boiling water and against leaching into the boiling water. Now, to provide a permanent seal, the panel is immersed in boiling water for 25 minutes.

In the treatments given above in each example, the panel was rinsed for about 30 seconds after each etching application and for about 15 seconds after each dyeing operation. Except for anodizing and final sealing, the

. time added by the different cycles of coloring treatments to the regular process for finishing uncolored anodized aluminum was about 30 minutes. However, by changing the strength of the solutions used, the process time may 1 be correspondingly varied.

It may also be observed that, after each sealing step, the period of time required for etching was increased. This increase in etching time, or an increase in the strength of the etching solution, is required because the heaviness of the overall seal increases with each additional sealing operation. Another factor, contributing to the need for increased etching action with successive color applications, is that some dyes, particularly the blacks and the blues, require sealing treatments of 3 or 4 minutes duration to render the dyes non-leachable.

The practice of the invention as described above is advantageous in several respects. As all of the treating liquids used in the process may be aqueous, the process may be more rapidly conducted than heretofore. The present process eliminates drying steps that must be included in many prior art processes, particularly those which alternate organic-liquid treatments with aqueous treatments. Since the liquid treatments in the present case are all aqueous, the work may be quickly prepared for the next liquid treatment by nothing more than a rinsing treatment. By using roll-printing and like techniques, the work may be etched quickly with a phasetype etching compound and sharp and accurate boundaries secured regardless of any intricacies in the pattern design.

It will of course be appreciated that the present invention is applicableto various other metals such as magnesium, titanium and tantalum.

Having described our invention, we claim:

1. A method of coloring a metal surface having a micro-porous anodic surface film formed by anodizing said metal surface, comprising: sealing said micro-porous anodic surface film with a seal of the hydration type to render the film non-absorbent of dye during a subsequent dyeing step; unsealing a portion of said film by selectively etching it leaving portions thereof unetched; dyeing said etched portion; and sealing said dyed portion. 5 2. The methodof claim 1 wherein: said etching step and said dyeing step are effected by aqueous media.

3. The method of claim 1 wherein: each of said steps is effected by contacting said surface film with an aqueous medium, and the etching step and the dyeing step are followed by aqueous rinsing treatments.

4. The method of claim 1 wherein: said last surface sealing step is carried to a stage providing a heavier relatively permanent and color fast seal.

5. The method of claim 1 wherein said last sealing step provides a seal of the hydration type, comprising: selectively etching said unetched portions of said film after said last sealing step; dyeing said second-etched portion; and sealing the film.

6. The method of claim 1 comprising: providing an aluminum surface coated with an oxide thereof as said metal surface and micro-porous film.

7. The method of'claim 6 comprising: at least one additional cycle of steps comprising etching, rinsing, dyeing and sealing in the order named wherein the sealing step of each cycle comprises immersing the article in a bath of from /2 to 1% solution of a compound from a group consisting of nickel acetate and cobalt acetate for at least one minute; and the sealing step of the last cycle includes immersion of said surface film in a water having a temperature of from 180 to 212 F. for a period of at least 20 minutes.

8. In a method of selectively coloring an anodized aluminum surface, the series of steps comprising: sealing the anodized aluminum surface with a seal of the hydration type to render said surface non-absorbent of dye during a subsequent dyeing step; unsealing a portion of said surface -by selectively etching it to render that portion absorbent; dyeing said absorbent portion with an /absorbent dye; and again sealing saidsurface with a seal of the hydration type.

References Cited in the file of this patent UNITED STATES PATENTS 2,127,885 Pettit Aug. 23, 1938 2,755,239 Glauser July 17, 1956 Patrick Nov. 5, 1957 

1. A METHOD OF COLORING A METAL SURFACE HAVING A MICRO-POROUS ANODIC DURFACE FILM FORMED BY ANODIZING SAID METAL SURFACE, COMPRISING: SEALING SAID MICRO-POROUS ANODIC SURFACE FILM WITH A SEAL OF THE HYDRATION TYPE TO RENDER THE FILM NON-ABSORBENT OF DYE DURING A SUBSEQUENT DYEING STEP; UNSEALING A PORTION OF SAID FILM BY SELECTIVELY ETCHING IT LEAVING PORTIONS THEREOF UNETCHED; DYEING SAID ETCHED PORTION; AND SEALING SAID DYE PORTION. 